If you received a link to join Crowds, but all you can see when you tap on it is your app's home screen, please make sure you're using version 4.5.1 or above of the iOS app and that you've enabled Crowds.
This feature is not yet available in the Android app.
If you're an Android user, you can upvote this post: https://1se.co/feedback/p/make-1se-crowds-available-on-android to let us know you'd like to see this in the app and to get updates about the status of that particular feature.
We are working on many great new features for our Android app. We have it on our roadmap, even though it will not be available in the next few updates.